1. Field of the Invention
The present invention relates to recycling polyolefins having a chlorine-containing polymer on at least one surface thereof. More specifically, the present invention relates to a method and a system of recycling polyolefins which includes removing a chlorine-containing polymer from the surfaces thereof prior to reprocessing the polyolefin.
2. Description of the Prior Art
Polyvinylidene chloride (PVdC) homopolymers and copolymers are chlorine-containing polymers that have excellent barrier properties to a wide variety of gases and liquids due to the combination of high density and high crystallinity in the polymers. Coated or extruded PVdC products with superior resistance to most gases, particularly oxygen, are used in packaging. The use of multipolymers of vinylidene chloride, as coatings or a coextruded layer for oriented polypropylene (OPP) materials has been recognized as an effective means for increasing the resistance of such film materials to the transmission of gases and vapors, such as oxygen and moisture vapor for example. Additionally, PVdC top-coating materials have been known to promote the heat sealability of such oriented film structures which, in an uncoated state, tend to seal only with great difficulty, if at all. PVdC coated oriented polypropylene is a particularly good packaging material for products which tend to be sensitive to attack by oxygen such as, for example, coffee and cheese, or snack foods such as corn-based products and potato chips.
Scrap is initially generated during the manufacture of the film, and secondarily when converters make the end product bag. Finally, scrap is available when the bagged product is consumed. With a commercially feasible recycle process, the film manufacturer would be able to blend the recycle into its main product lines. Even with ink and other coatings, the scrap of the converter and the consumer would be recyclable into many useful products such as carpet backing, park benches, office furniture, signs, battery cases, coat hangers, synthetic lumber and other construction material.
However, these PVdC materials are thermally unstable, with thermal degradation by evolving HCl due to dehydrochlorination starting at temperatures as low as 120.degree. C. While extruding recycled polypropylene containing a PVdC on conventional equipment, thermal degradation can cause problems. For example, the evolving HCl is harmful to personnel and HCl can cause corrosive wear of the extrusion equipment. Further, discoloration, voids, and black specs are found in the product as a result of the PVdC which will downgrade the quality of the recycled product.
U.S. Pat. Nos. 4,643,861 and 4,877,821 disclose methods of preparing recyclable blends including thermally sensitive vinylidene chloride by adding a stabilizing or neutralizing agent to the blend before extrusion or molding. It appears that these patents seek to react and neutralize HCl after it is generated.